NewsDrop-Winter-2021

Illustration: San Marcos Gambusia.

“THE IMPORTANT POINT TO ALL OF THIS IS THAT EVEN THOUGH THE SAN MARCOS GAMBUSIA IS GONE FROM TEXAS AND PLANET EARTH, WE SHOULD MAKE SURE THAT ITS EXTINCTION FROM THE SAN MARCOS RIVER IS NOT FORGOTTEN. THAT WILL HELP US ENSURE ENDURES, AND THAT ALL OF US CONTINUE TO PUT FORTH EVERY EFFORT TO SAVE OTHER SPECIES THAT ARE IN DANGER OF EXTINCTION.” THAT THE NATURAL HERITAGE OF TEXAS

In reviewing the species specific to the Edwards Aquifer, USFWS Biologist Paige Najvar says the most important things they look at are all of the threats that the species face. “For the Edwards Aquifer species, we understand that this is the only place in the world they exist, meaning that if something ever happened to the aquifer, the endangered species and others could be gone forever. Additionally, we consider the amount of water being pumped from the Edwards Aquifer now and amounts needed for the future, how water quality is being maintained, and other conditions that might threaten the water quality and quantity needed to preserve the endangered species.” When it comes to the San Marcos gambusia, fellow biologist with Najvar in the Austin Ecological Services Field Office, Donelle Robinson, explained that the species was proposed for listing as endangered in 1978. At the time, the fish was already rare with an estimated population of about 1,000 fish. “The San Marcos gambusia was officially listed as endangered in 1980. At that time, there were several focused efforts to find Gambusia in the San Marcos River and increase their population in captivity.

However, all of those attempts were not successful. Around the 1990 timeframe, another extensive survey of portions of the San Marcos River was conducted to see if there might be any San Marcos gambusia still living. That work also came up empty. We reviewed all of that program data and reporting before we made the decision to propose delisting the San Marcos gambusia due to extinction. We are currently in the comment phase of the process and that will give us essentially one last opportunity to see if there is any information out there that would warrant us reconsidering the removal of the San Marcos gambusia from the endangered species list.” Kevin Mayes, the Texas Parks and Wildlife Department Native Fish Conservation Coordinator, was a part of the team that scoured the San Marcos River in 1990 in what would be a final effort to locate a San Marcos gambusia. “It was definitely quite the excursion. There were at least a couple of dozen fish biologists with seines and dip nets on the hunt for the San Marcos gambusia. Over the course of a few days, we collected thousands of Gambusia. We took them to the federal fish hatchery in San Marcos where each fish was examined by experts like Bob Edwards and Clark Hubbs.

Only a few potential hybrids were found, but there were no pure San Marcos gambusia, only Western Mosquitofish and Largespring Gambusia which are also native to the river.” When asked what could have caused the loss of the San Marcos gambusia, Mayes said, “There are some theories that say the non-native elephant ear plants that once blanketed the San Marcos River essentially crowded out the San Marcos gambusia. But, there are probably a number of factors, such as a long history of dam construction, urban runoff increasing with the growth of San Marcos, the channelization of some parts of the river and the introduction of additional exotic, non-native plants that led to changes in habitat for the San Marcos gambusia.” Mayes’ final thoughts about the San Marcos gambusia were essentially a call to action on the part of citizens and biologists alike. He said that more than 40 percent of America’s freshwater fishes are imperiled and subject to possibly being listed on the federal endangered species list.

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